certain facts and info on os

2. 


The operating system (OS) is the first thing
loaded onto the computer -- without the
operating system, a computer is useless.
operating systems can now be found on many
of the devices we use every day, from cell
phones to wireless access points.
The purpose of an operating system is to
organize and control hardware and software
so that the device it lives in behaves in a
flexible but predictable way.

3. Not all computers have operating systems. The
computer that controls the microwave oven in your
kitchen, for example, doesn't need an operating
system. It has one set of tasks to perform, very
straightforward input to expect (a numbered keypad
and a few pre-set buttons) and simple, neverchanging hardware to control.
For a computer like this, an operating system
would be unnecessary baggage, driving up the
development and manufacturing costs significantly
and adding complexity where none is required.
Instead, the computer in a microwave oven simply
runs a single hard-wired program all the time.

4. 
All desktop computers have
operating systems. The most common are the
Windows family of operating systems
developed by Microsoft, the Macintosh
operating systems developed by Apple and
the UNIX family of operating systems (which
have been developed by a whole history of
individuals, corporations and collaborators).
There are hundreds of other operating
systems
available
for
special-purpose
applications, including specializations for
mainframes, robotics, manufacturing, realtime control systems and so on.

5. 

Operating system are made of portable code
instead of permanent physical circuits so that
changes can be made regularly as an when
required without scrapping the whole device
For a desktop computer user, this means you
can add a new security update, system patch,
new application or even an entirely new
operating system rather than junk your
computer and start again with a new one
when you need to make a change.

7. 





Processor management
Memory management
Device management
Storage management
Application interface
User interface

8. SYSTEM
COMPONENTS
These are the pieces of the system we’ll be looking at:
Process Management
Main Memory Management
File Management
I/O System Management
Secondary Management
Networking
Protection System
Command-Interpreter System
2: OS Structures
8

9. SYSTEM
COMPONENTS
PROCESS MANAGEMENT
A process is a program in execution: (A program is passive, a process
active.)
A process has resources (CPU time, files) and attributes that must be
managed.
One (or more) threads are the schedulable entities within a process.
Management of processes includes:
Thread Scheduling (priority, time management, . . . )
Creation/termination
Block/Unblock (suspension/resumption )
Synchronization
Communication
Deadlock handling
Debugging
2: OS Structures
9

10. System
Components
MAIN MEMORY MANAGEMENT
Allocation/de-allocation for processes, files, I/O.
Maintenance of several processes at a time
Keep track of who's using what memory
Movement of process memory to/from secondary storage.
FILE MANAGEMENT
A file is a collection of related information defined by its creator.
Commonly, files represent programs (both source and object forms)
and data.
The operating system is responsible for the following activities in
connections with file management:
• File creation and deletion.
• Directory creation and deletion.
• Support of primitives for manipulating files and directories.
• Mapping files onto secondary storage.
• File backup on stable (nonvolatile) storageOS Structures
2: media.
10

11. System
Components
I/O MANAGEMENT
Buffer caching system
Generic device driver code
Drivers for each device - translate read/write requests into disk
position commands.
SECONDARY STORAGE MANAGEMENT
Disks, tapes, optical, ...
Free space management ( paging/swapping )
Storage allocation ( what data goes where on disk )
Disk scheduling
2: OS Structures
11

12. System
Components
NETWORKING
Communication system between distributed processors.
Getting information about files/processes/etc. on a remote
machine.
Can use either a message passing or a shared memory model.
PROTECTION
Of files, memory, CPU, etc.
Means controlling of access
Depends on the attributes of the file and user
How Do These All Fit
Together?
In essence, they all
provide services for
each other.
SYSTEM PROGRAMS
Command Interpreters
-- Program
statements (shell, GUI interface, etc.)
that
accepts
control
Compilers/linkers
Communications (ftp, telnet, etc.)
2: OS Structures
12

13. 
It manages the hardware and software
resources of the system. In a desktop
computer, these resources include such
things as the processor, memory, disk space
and more (On a cell phone, they include the
keypad, the screen, the address book, the
phone dialer, the battery and the network
connection).

14. 



It provides a stable, consistent way for applications to
deal with the hardware without having to know all the
details of the hardware.
A consistent application program interface (API)
allows a software developer to write an application on
one computer and have a high level of confidence
that it will run on another computer of the same type,
even if the amount of memory or the quantity of
storage is different on the two machines.
Operating system must also ensure that the
application should continue to run even if there is a
hardware upgrade, data migrates on different device
etc.
One of the challenges facing developers is keeping
their operating systems flexible enough to run
hardware from the thousands of vendors
manufacturing computer equipment. Today's systems
can accommodate thousands of different printers,
disk drives and special peripherals in any possible
combination.

15. 
Based on Environment
◦ CUI
◦ GUI

Based on Functions
◦
◦
◦
◦
◦
◦
◦
◦
◦
Real-time operating system
Single-user, single task
Single-user, multi-tasking
Multi-user , multi-tasking
Multiprocessing O/S
Multithreading O/S
Networking O/S
Batch Processing O/S
Distributed O/S

16. 
This operating system is totally command
dependent. One can work on this
environment only if they are familiar with the
respective O/S command
◦ Eg. MS-DOS

17. 

GUI - Short for Graphical User Interface, a GUI
Operating System contains graphics and
icons and is commonly navigated by using a
computer mouse. See the GUI definition for a
complete definition. Below are some
examples of GUI Operating Systems.
System 7.x
Windows 98
Windows CE

18. 

RTOS is specially designed for embedded
environments such as consumer devices,
automobiles and robotics.
A real-time operating system (RTOS) is an
operating system (OS) intended to serve realtime application requests. It must be able to
process data as it comes in, typically without
buffering
delays.
Processing
time
requirements (including any OS delay) are
measured in tenths of seconds or shorter.

19. 


RTOS) - Real-time operating systems are used to
control machinery, scientific instruments and
industrial systems.
An RTOS typically has very little user-interface
capability, and no end-user utilities, since the
system will be a "sealed box" when delivered for
use.
A very important part of an RTOS is managing
the resources of the computer so that a particular
operation executes in precisely the same amount
of time, every time it occurs.

20. 







A common example of an RTOS is an HDTV receiver
and display. It needs to read a digital signal, decode
it and display it as the data comes in. Any delay
would be noticeable as jerky or pixelated video
and/or garbled audio.
Some of the best known, most widely deployed, realtime operating systems
LynxOS
OSE
QNX
RTLinux
VxWorks
Windows CE

21. 

As the name implies, this operating system is
designed to manage the computer so that
one user can effectively do one thing at a
time. The Palm OS for Palm handheld
computers is a good example of a modern
single-user, single-task operating system.
EG. MS-DOS

22. 


An example of a this kind of O/S would be the
O/S of a basic mobile phone or an mp3 player.
There can only be one user using the device and
that person is only using one of its applications
at a time
An MP3 player contains a computer to handle all
of its functions. It has a small amount of memory
and a number of specialist silicon chips . The
operating system is installed in memory and runs
as soon as you switch on the device.

23. 

This is the type of operating system most people
use on their desktop and laptop computers
today. Microsoft's Windows and Apple's MacOS
platforms are both examples of operating
systems that will let a single user have several
programs in operation at the same time. For
example, it's entirely possible for a Windows user
to be writing a note in a word processor while
downloading a file from the Internet while
printing the text of an e-mail message.
Another word for multi-tasking is
multiprogramming
◦ E.g. Windows 95.

24. 
A multi-user operating system allows many
different users to take advantage of the
computer's resources simultaneously. The
operating system must make sure that the
requirements of the various users are balanced,
and that each of the programs they are using has
sufficient and separate resources so that a
problem with one user doesn't affect the entire
community of users. Unix, VMS and mainframe
operating systems, such as MVS, are examples of
multi-user operating systems.

25. 
Examples of this kind of O/S include various
versions of UNIX, LINUX, IBM’s z/OS, OS390,
MVS and VM

26. 


Operating system that supports networking
examples of a network O/S include Windows
Vista, Windows 8 and Mac O/S X , Unix, Linux
and all other mainframes O/S
A network O/S system should have the
following features :◦ Deal with users logging on
◦ Maintain the network connection to the sercver
◦ Expand the file system to view folders on other
computers
◦ Provide security to separate user accounts from
each other

28. 


This is one of the modern operating system
It is a O/S that supports distributed
computing
Distributed systems allow users to share
resources on geographically dispersed hosts
connected via a computer network. Services
could be provided either through a ClientServer Model or a Peer-to-Peer model

29. 


A distributed system is a collection of loosely
coupled processors interconnected by a
communication network.
The processors in a distributed system may
vary in size and function. They may include
microprocessors, workstations,
minicomputers and large general purpose
computer systems
They are referred as sites, nodes, computers,
machines and hosts

30. 
There are two types distributed System
◦ Parallel Computing
◦ Distributed Computing

31. 



In the most simple form = Parallel Computing is a method
where several individual (autonomous) systems (CPU's)
work in tandem to resolve a common computing workload.
Distributed Computing is where several dis-associated
systems are working separately to resolve a multi-faceted
computing workload.
An example of Parallel computing would be two servers
that share the workload of routing mail, managing
connections to an accounting system or database, solving
a mathematical problem, etc....
Distributed Computing would be more like the SETI (Search
for extra-terresterial intelligence). Program, where each
client works a separate "chunk" of information, and returns
the completed package to a centralized resource that's
responsible for managing the overall workload.
If you think of ten men pulling on a rope to lift a load, that
is parallel computing. If ten men have ten ropes and are
lifting ten different loads from one place to consolidate at
another place, that would be distributed computing.
In Parallel Computing all processors have access to a
shared memory. In distributed computing, each processor
has its own private memory

32. 



Resource Sharing
Computation Speedup
Reliability
Communication

33. 
If number of different sites are connected to
one another, then a user at one site may be
able to use the resources available at another.
For. E.g. a user at site A may be using a laser
printer located at site B

34. 

If a particular computation can be partitioned
into subcomputations that can run
concurrently then a distributed system allows
us to distribute the subcomputations among
various sites.
There also exist automated load sharing in
which the distributed operating system
automatically moves jobs among several
sites that are lightly loaded.

35. 

If one site fails in a distributed system the
remaining sites can continue operating giving
the system better reliability.
Data is replicated among several sites in a
distributed system so that even if one site
fails data still can be access from other sites.

36. 
When several sites are connected to one
another by a communication network, the
users at different sites have the opportunity
to exchange information like pass message
among themselves, collaborate on project by
transferring the files of the project, logging in
to each other’s remote systems to run
programs and exchanging mail to coordinate
the work.

37. 
With the advent of computer networks, in
which many computers are linked together
and are able to communicate with one
another, distributed computing became
feasible. A distributed computation is one
that is carried out on more than one machine
in a cooperative manner. A group of linked
computers working cooperatively on tasks,
referred to as a distributed system, often
requires a distributed operating system to
manage the distributed resources

38. The operating systems commonly used for
distributed computing systems can be broadly
classified into two types
–Network operating systems
-Distributed operating systems.
The three most important features commonly
used to differentiate between these two types of
operating systems are
o
System image,
o
Autonomy, and
o
Fault tolerance capability.


39. 

System image: Under network OS, the user
views the distributed system as a collection of
machines connected by a communication
subsystem. i.e the user is aware of the fact
that multiple computers are used. A
distributed OS hides the existence of multiple
computers and provides a single system
image to the users.
Autonomy: A network OS is built on a set of
existing centralized OSs and handles the
interfacing and coordination of remote
operations and communications between
these OSs. So, in this case, each machine has
its own OS. With a distributed OS, there is a
single system-wide OS and each computer
runs part of this global OS.

40. Fault tolerance capability: A network operating
system provides little or no fault tolerance
capability in the sense that if 10% of the
machines of the entire distributed computing
system are down at any moment, at least 10% of
the users are unable to continue with their work.
On the other hand, with a distributed operating
system, most of the users are normally
unaffected by the failed machines and can
continue to perform their work normally, with
only a 10% loss in performance of the entire
distributed computing system.
Therefore, the fault tolerance capability of a
distributed operating system is usually very high as
compared to that of a network operating system


41. 



Real Time Embedded Systems
Multimedia Systems
Handheld Systems
Clustered Systems

42. 
http://www.cs.uni.edu/~mccormic/RealTime/
what.html
◦ E.g. ABS(Antilock Breaking Systems) and Security
Systems in Automobiles

43. 
Supports multiple kinds of applications
◦ Multimedia applications : Streaming audio, video
games, etc.
◦ Traditional applications : Editors, compilers, web
servers, etc.
◦ Different applications have different requirements
For e.g. interactive applications like Editors,
compilers require low or average response time
◦ While soft real time applications like streaming
media , virtual games requires high response time
◦ Multimedia O/S divides resources according to
application requirements. E.g. 30 % of CPU to
streaming and 20% to http server,… etc.

44. 



Multimedia data consist of audio and video files
as well as conventional files.
These data differ from conventional data in that
multimedia data such as frame of video must be
delivered according to certain time restrictions
(for e.g., 30 frames per second)
Multimedia applications may also include live
webcasts(broadcast over the world wide web) of
speeches or sporting events and even live
webcams that allow a viewer n Manhattan to
observe customers at a café in Paris.
Multimedia applications also run on smaller
devices. Eg. Stock trader may have stock quotes
delivered wirelessly and in real time to his PDA.

45. 

A mobile operating system, also referred to
as mobile OS, is the operating system that
operates a smartphone, tablet, PDA, or other
digital mobile devices. Modern mobile
operating systems combine the features of a
personal computer operating system with a
touchscreen, cellular, Bluetooth, WiFi, GPS
mobile navigation, camera, video camera,
speech recognition, voice recorder, music
player, Near field communication, Infrared
Blaster, and other features.
E.g. Android from google inc., Blackberry10
from Blackberry, iOS from Apple Inc. Nokia
Asha Platform from Nokia, Symbian OS from
Nokia etc.

46. 
Cluster computing is a type of distributed computing. Distributed
computing just means coordinating a number of computers to
accomplish a single task. Cluster computing means the
computers are specifically organized just to work together to
accomplish a single task.
For example, massively parallel "grid computing" projects like
seti@home and folding@home are examples of distributed
computing but they are not cluster computing. Here, the
computers all work together to accomplish a task, so this is
distributed computing. But they are not specifically arranged for
this purpose (the arrangement is haphazard and uncoordinated
with computers all over the place being randomly added and
removed from the set working on the problem), so they are not a
cluster and this is not cluster computing.

47. 

What is SETI@home?
SETI@home is a scientific experiment that uses Internetconnected computers in the Search for Extraterrestrial
Intelligence (SETI). You can participate by running a free
program that downloads and analyzes radio telescope data.
E.g. http://setiathome.berkeley.edu/sah_about.php
Folding@home (FAH or F@h) is a distributed computing
project for disease research that simulates protein folding,
computational drug design, and other types of molecular
dynamics. The project uses the idle processing resources of
thousands of personal computers owned by volunteers who
have installed the software on their systems. Its primary
purpose is to determine the mechanisms of protein folding,
which is the process by which proteins reach their final
three-dimensional structure, and to examine the causes of
protein misfolding.

48. 
A clustered system uses multiple CPUs to complete a task. It is different from
parallel system in that clustered system consists of two or more individual systems
tied together. The clustered computers share storage and are closely linked via LAN
networking.
The clustering is usually performed to provide high availability. A layer of cluster
software runs on cluster nodes. Each node can monitor one or more nodes over the
LAN.
The monitored machine can fail in some cases. The monitoring machine can take
ownership of its storage. The monitoring machine can also restart applications that
were running on the failed machine- The failed machine can remain down but the
users will see a brief of the service.
The clustered system can be of the following forms:
• Asymmetric Clustering: In this form, one machine is in hot standby mode and
other machine is running the application. The hot standby machine performs
nothing. It only monitors the server. It becomes the active server if the server fails.
• Symmetric Clustering: In this mode, two or more machines run the applications.
They also monitor each other at the same time. This mode is more efficient because
it uses all available machines. It can be used only if multiple applications are
available to be executed.

49. 



Client Server
Peer to Peer
Web Based Computing
Cloud Computing

50. 
Embedded means that a computer is
embedded in the device - like a car or a
microwave oven.
Web-based computing puts the program on
the web site - like Google documents.
Traditional computing is a traditional
computer (keyboard, screen, etc.) with the
applications running, and the data stored, on
the computer.

51. 

Where once all the talk about personal computing
was based on desktop, laptop or notebook
computers, all of which ran applications locally,
now it seems, the buzz is all about web based
computers - smartphones, tablets, Chromebooks
and more recently, the Surface Tablet from
Microsoft.
It's subtle, yet suddenly, inevitable. As surely as
we bought a personal computer before, now
we're all pondering the choices of web based
computers, even as some wonder what the
difference is. The short answer is that they are
computers with weaker processors and no hard
drives that run applications off the "cloud instead
of locally and generally have touch screens to
make using them easier. They're also generally
lighter and smaller than so-called "real"
computers.

52. WHY WEB BASED COMPUTING

That answer is just as easy - because they are
cheaper. Computers cost less if you don't have to
have to include a hard drive. They also cost less if
you don't have to buy and install software on
them, and that is the real driving force behind the
switch. Less obvious is that users can use more
than one of them rather seamlessly. Consider the
new Surface Tablet from Microsoft. It runs a webcomputer based version of Windows that looks
virtually identical to Windows 8 which runs on real
computers. This means users don't have to learn
two systems. But it means more than that, it
means that users can use web, or cloud based
apps instead of those they install locally, e.g.
Google Docs, Facebook, Flickr, etc. to create,
manipulate and store their work, which they can
then access using their phone, Chromebook, or
any other web based device.

53. 

All of this is evident as reports of a slowdown
in sales of real computers contrasts with
those noting bigger numbers for iOS, Android
and now Windows 8/RT based machines,
which are essentially all the same breed:
computers that do little except allow users to
browse the web, access social media and play
music or video files.
It's the newest trend in personal computing,
and it's been going on for long enough now,
that most have heard the rumblings.

54. 


In science, cloud computing is a synonym for
distributed computing over a network and
means the ability to run a program on many
connected computers at the same time.
Cloud computing is a type of computing that
relies on sharing computing resources rather
than having local servers or personal devices
to handle applications.
It is called cloud computing because the data
and applications exist on a “cloud” of WEB
servers.

55. 



ASSEMBLERS
COMPILERS
INTERPRETERS
LINKERS

56. 

A program that translates programs from
assembly language to machine language.
An assembler is a program that takes basic
computer instructions and converts them into
a pattern of bits that the computer's
processor can use to perform its basic
operations. Some people call these
instructions assembler language and others
use the term assembly language.

57. 
Most computers come with a specified set of very
basic instructions that correspond to the basic
machine operations that the computer can
perform. For example, a "Load" instruction
causes the processor to move a string of bits
from a location in the processor's memory to a
special holding place called a register. Assuming
the processor has at least eight registers, each
numbered, the following instruction would move
the value (string of bits of a certain length) at
memory location 3000 into the holding place
called register 8: L 8,3000

58. 




The programmer can write a program using a
sequence of these assembler instructions.
This sequence of assembler instructions, known
as the source code or source program, is then
specified to the assembler program when that
program is started.
The assembler program takes each program
statement in the source program and generates a
corresponding bit stream or pattern (a series of
0's and 1's of a given length).
The output of the assembler program is called
the object code or object program relative to the
input source program. The sequence of 0's and
1's that constitute the object program is
sometimes called machine code.
The object program can then be run (or
executed) whenever desired.

59. 
Today, assembler programming is used only
where very efficient control over processor
operations is needed. It requires knowledge
of a particular computer's instruction set,
however.

60. 

Historically, most programs have been written in
"higher-level" languages such as COBOL,
FORTRAN, PL/I, and C. These languages are
easier to learn and faster to write programs with
than assembler language. The program that
processes the source code written in these
languages is called a compiler.
A compiler is a program that translates a source
program written in some high-level
programming language (such as Java) into
machine code for some computer architecture
(such as the Intel Pentium architecture). The
generated machine code can be later executed
many times against different data each time.

61. 
A program that translates source code into object
code. The compiler derives its name from the
way it works, looking at the entire piece of
source code and collecting and reorganizing the
instructions. Thus, a compiler differs from an
interpreter, which analyzes and executes each
line of source code in succession, without
looking at the entire program. The advantage of
interpreters is that they can execute a program
immediately. Compilers require some time before
an executable program emerges. However,
programs produced by compilers run much faster
than the same programs executed by an
interpreter.

62. 
Because compilers translate source code into
object code, which is unique for each type of
computer, many compilers are available for
the same language. For example, there is a
FORTRAN compiler for PCs and another for
Apple Macintosh computers. In addition, the
compiler industry is quite competitive, so
there are actually many compilers for each
language on each type of computer. More
than a dozen companies develop and sell C
compilers for the PC.

63. 


A program that executes instructions written in a high-level language.
There are two ways to run programs written in a high-level language.
The most common is to compile the program; the other method is to
pass the program through an interpreter.
An interpreter translates high-level instructions into an intermediate
form, which it then executes. In contrast, a compiler translates highlevel instructions directly into machine language. Compiled programs
generally run faster than interpreted programs. The advantage of an
interpreter, however, is that it does not need to go through the
compilation stage during which machine instructions are generated. This
process can be time-consuming if the program is long. The interpreter,
on the other hand, can immediately execute high-level programs. For
this reason, interpreters are sometimes used during the development of
a program, when a programmer wants to add small sections at a time
and test them quickly. In addition, interpreters are often used in
education because they allow students to program interactively.
Both interpreters and compilers are available for most high-level
languages. However, BASIC and LISP are especially designed to be
executed by an interpreter. In addition, page description languages,
such as PostScript, use an interpreter. Every PostScript printer, for
example, has a built-in interpreter that executes PostScript instructions.

64. 

Also called link editor and binder, a linker is a
program that combines object modules to form
an executable program. Many programming
languages allow you to write different pieces of
code, called modules, separately. This simplifies
the programming task because you can break a
large program into small, more manageable
pieces. Eventually, though, you need to put all
the modules together. This is the job of the
linker.
In addition to combining modules, a linker also
replaces symbolic addresses with real addresses.
Therefore, you may need to link a program even
if it contains only one module.

71. Operating system
Date first released
Platform
Developer
AIX and AIXL
Unix and Linux history.
Various
IBM
AmigaOS
Currently no AmigaOS
history.
Amiga
Commodore
BSD
Unix and Linux history.
Various
BSD
Caldera Linux
Unix and Linux history.
Various
SCO
Corel Linux
Unix and Linux history.
Various
Corel
Debian Linux
Unix and Linux history.
Various
GNU
DUnix
Unix and Linux history.
Various
Digital
DYNIX/ptx
Unix and Linux history.
Various
IBM
HP-UX
Unix and Linux history.
Various
Hewlett Packard
IRIX
Unix and Linux history.
Various
SGI
Kondara Linux
Unix and Linux history.
Various
Kondara
Linux
Unix and Linux history.
Various
Linus Torvalds

72. MAC OS 8
Apple operating
system history.
Apple Macintosh Apple
MAC OS 9
Apple operating
system history.
Apple Macintosh Apple
MAC OS 10
Apple operating
system history.
Apple Macintosh Apple
MAC OS X
Apple operating
system history.
Apple Macintosh Apple
Mandrake Linux
Unix and Linux
history.
Various
Mandrake
MINIX
Unix and Linux
history.
Various
MINIX
MS-DOS 1.x
MS-DOS history.
IBM
Microsoft
MS-DOS 2.x
MS-DOS history.
IBM
Microsoft

73. MS-DOS 3.x
MS-DOS history.
IBM
Microsoft
MS-DOS 4.x
MS-DOS history.
IBM
Microsoft
MS-DOS 5.x
MS-DOS history.
IBM
Microsoft
MS-DOS 6.x
MS-DOS history.
IBM
Microsoft
NEXTSTEP
Apple operating
system history.
Various
Apple
OSF/1
Unix and Linux
history.
Various
OSF
QNX
Unix and Linux
history.
Various
QNX
Red Hat Linux
Unix and Linux
history.
Various
Red Hat
SCO
Unix and Linux
history.
Various
SCO
Slackware Linux
Unix and Linux
history.
Various
Slackware

74. Windows 3.X
Microsoft
Windows history.
IBM
Microsoft
Windows 8
Microsoft
Windows history.
IBM
Microsoft
Windows 7
Microsoft
Windows history.
IBM
Microsoft
Windows 95
Microsoft
Windows history.
IBM
Microsoft
Windows 98
Microsoft
Windows history.
IBM
Microsoft
Windows CE
Microsoft
Windows history.
PDA
Microsoft
Windows ME
Microsoft
Windows history.
IBM
Microsoft
Windows NT
Microsoft
Windows history.
IBM
Microsoft

75. Windows 98
Microsoft
Windows
history.
IBM
Microsoft
Windows CE
Microsoft
Windows
history.
PDA
Microsoft
Windows ME
Microsoft
Windows
history.
IBM
Microsoft
Windows NT
Microsoft
Windows
history.
IBM
Microsoft
Windows Vista
Microsoft
Windows
history.
IBM
Microsoft
Windows XP
Microsoft
Windows
history.
IBM
Microsoft
Unix and Linux